The James Webb Space Telescope: a new sense of wonder
With the release of the first photo on July 12, NASA confirmed the proper functioning of the new telescope, a concentration of technology and perfection where the error or failure of a single mechanism would compromise the entire project.
Raise your hand if you have not felt a sense of wonder at the first image sent back from the James Webb Space Telescope (JWST). An image that depicts a very distant portion of the universe, nearly 14 billion light years, a few million years after the big bang. The telescope will enable it to gather valuable information useful in taking a step toward understanding a mystery that grips all space scholars-the birth of the universe.
Let’s be clear, in its 30 years of honored service, its predecessor, the Hubble telescope, has transmitted so many images of deep space. But its technology, despite upgrades, cannot get as far as Webb can. That is why its implementation was necessary. To go even deeper into the discovery of the unknown. The JWST is much more powerful than previous or telescopes sent into orbit. It is 110 times more powerful than Hubble; much larger but lighter. It was built to see the first stars and galaxies that emerged from the dust and gas clouds of the early universe.
How is it different from its predecessors
To investigate deep space and detect the most distant light that turns red, that of the most ancestral celestial bodies, Webb uses the wavelengths of infrared light. Not that this technology was not already in use. Terrestrial telescopes and even the latest Hubble upgrades use it successfully, but only in the near-infrared wavelength, not the full range. On Earth, infrared is disturbed by the atmosphere and terrestrial and solar radiation. In addition, a temperature of use close to absolute zero is required to make the best use of this technology. Hubble is stationed in Earth’s orbit at a distance of 547 km, and under these conditions, the use of infrared is not optimal.
To obviate terrestrial, lunar and solar radiation, the Webb telescope has been sent 1.5 million km away from Earth, to the L2 point, or second Lagrange point, 4 times farther than the Moon. This will bring its orbit in line with Earth as it moves around the Sun. Not only that, Earth will act as its shield and provide it with great protection from heat and light. In addition, the position at the second Lagrange point, always the same toward Earth, will make communications with the command station easy and continuous. Communications are handled through the Deep Space Network via three large antennas located in Australia, Spain and California. In this way, it will always be possible to send and receive data. The JWST telescope took 30 days to reach the L2 point, during which time it completed the deployment procedure of all its components.
A telescope far away
This distance from Earth presents a major drawback. Hubble was sent into space with an unexpected defect. They noticed it by observing the first images. Something in the smoothing of the mirror had gone wrong. But the telescope was rotating around Earth’s orbit, and thanks to the Space Shuttle, it was possible to intervene and insert parts to correct the error. Since it was sent into orbit in 1990, again carried by shuttle, there have been five repairs and upgrade missions. With Webb, on the other hand, this is not possible, an error is not allowed and everything must work perfectly, any deployment mechanism, communication, rotation, and detection.
If just one of the 144 mechanisms used to deploy the mirror and heat shield had not worked properly, the mission would have been lost. The JWST was stowed inside a carrier rocket, folded like origami. This was the most complicated part of the mission, the part with the highest failure rate. Eighty percent of the chances of failure of the operation were related to the deployment stages, particularly of the protective shield.
How a disruptive technology is born…
The genesis of the Webb telescope began in the 1990s. It took about 30 years of study, research, funding and testing to launch it into space with the Ariane 5 rocket, the only one big enough to carry it. To house it inside the rocket, it was designed as a folding telescope, just like origami. Several innovative technologies were developed for the JWST.
The mirror is 6.5 meters in diameter and consists of 18 hexagonal mirrors made of ultralight beryllium side by side in a honeycomb pattern and coated with a 100-nanometer-thick layer of gold, the best material for reflecting infrared light. The gold foil is in turn covered with a thin layer of silica to protect it from scratches or small particles. Behind each hexagonal screen is a motor that aligns the mirror with the others with nanometer-level precision.
The optical system also consists of the secondary mirror placed in front of the primary mirror and supported by a three-foot structure and the optical subsystem, a mirror that removes astigmatism, flattens the focal field, and enables the production of images without optical aberrations, placed in the center of the primary mirror. An additional mirror has the function of directing light to the instruments. Another feature is the large 5-layer rhomboidal shielding (separated by vacuum) made of Kapton, a plastic film material that, like a sunshade, attenuates heat and provides stability to considerable thermal variations.
…and how it works.
Each layer is separated by insulating vacuum that dissipates heat while keeping each layer cooler than the previous one. The layers are coated with aluminum and doped silicon to promote their optical, conductive and durability properties. To detect more distant infrared signals, the telescope must be protected from any source of light and heat. Even from its instruments, which can generate heat, such as the solar panel, antenna, and computer. The protective shield, the size of a tennis court, allows the mirrors to operate at a temperature of 225 degrees celsius below zero. The difference with the side exposed to the sun is enormous. If you can freeze nitrogen on one side, you can boil water, at 85 degrees Celsius. The deployment of the sunscreen was the most complex part of the mission. If it was not fully deployed, the telescope would not work.
It is also extremely resistant to meteor bombardment. The shield is part of the spacecraft system that includes the solar panels to power the structure, the spacecraft bus, which is the spacecraft with propellant for movement, and other communication, control and orientation tools. The third main element that makes up the telescope is the ISIM (Integrated -Science Instrument Module). It includes the science instrumentation consisting of the MIRI, an instrument for observation and spectroscopic analysis at mid-infrared wavelengths, optimal for direct visualization of hot exoplanets and analysis of their atmospheres by spectroscopy.
It is an instrument so sensitive that it could detect a candle on a moon of Jupiter 700 million kilometers from Earth. The NIRSpec is a spectrograph for detecting near-infrared, and the NIRCam is an infrared camera. This facility is equipped with a cryogenic facility to cool the mid-infrared detectors and mounts innovative micro-obturators that allow the selection of certain spectra of light allowing analysis of up to 100 objects simultaneously in deep space at a light-gathering rate significantly faster than Hubble.
Costs and mission
It should not be assumed that the JWST is a delicate facility. Debris and meteorite remnants travel through space. The telescope has already been hit five times by debris, the last of which had a small mark on the primary mirror, but this has not affected its operation. Also because the nearest repair center is 1.5 km away, not exactly around the corner. For this reason, only the space simulation phase lasted 100 days, under conditions similar to operating conditions, at minus 217 degrees Celsius and in a gravity-free environment. The space simulations were carried out in the chamber used to test the Apollo missions. While the entire multiple testing phases on all instruments lasted six years. Two decades were spent building and trying each one, a million times.
In total, the JWST cost NASA about $11 billion, well above initial projections. The mission will last between 5 and 10 years. But why is this mission so important? The answer is to study wavelengths in the infrared bar. As the Universe is constantly expanding, light from bodies in receding deep space also tends to shift, thus reaching the detector with reduced frequency. Astronomers call this phenomenon redshift. These objects are therefore more easily detected when observed with instruments optimized for studying infrared frequencies.
Infrared observations allow the study of objects and regions of space otherwise obscured by gas and dust in the visible spectrum. Infrared penetrates gas and dust clouds better than other wavelengths. Star and planet formation usually occurs in the midst of these clouds. In addition, infrared lends itself very well with spectroscopy, which allows us to analyze the chemical composition of stars and atmospheres and identify planets where life is possible.
If you are interested in Space, the School of Disruption has many courses on the subject, especially after the partnership with International Space University. Here a webinar about Space and the future of work.